Compound light receiving elements for exposure meters

ABSTRACT

A photometric device for generating an electric signal related to coincident light intensity comprises a number of photoresponsive means each including first and second photoconductive elements having response characteristics such that the logarithm of resistance to the logarithm of light intensity are respectively proportional over different ranges of light intensity. Additionally, the first photoconductive element in each of the photoresponsive means has a higher sensitivity than that of the second photoconductive element. The first and second photoconductive elements are positioned to receive light for different areas of the objective field. The first and second photoconductive element of each photoresponsive means are specifically interconnected with similar elements of another photoresponsive means to enhance the light response characteristics.

United States Patent [191 Tsujimoto et al.

[ COMPOUND LIGHT RECEIVING ELEMENTS FOR EXPOSURE METERS [75] Inventors: Kayoshi Tsujimoto, Osaka; Kotaro Yata, lkeda; Motonobu Matsuda,

Sakai, all of Japan [73] Assignee: Minolta Camera Kabushiki Kaisha,

Osaka-shi, Osaka-fu, Japan [22] Filed: Dec. 6, 1971 [21] App]. No.: 204,832

[30] Foreign Application Priority Data Dec. 10, 1970 Japan 45/109168 [52] US. Cl. 95/10 C, 95/42 R, 356/222 [51] Int. Cl. ..G01j l/52 [58] Field of Search 95/10 C, 10 CT, 42 R; v 356/222 [56] References Cited UNITED STATES PATENTS 3,450,016 6/1969 Yamada 356/222; 3,529,893 9/1970 Holle et al. 95/10 C. 2/1966 Stimson 95/10 C,

Primary Examiner.loseph F. Peters, Jr. Assistant Examiner-Russell E. Adams, Jr. Attorney-Watson, Cole, Grindle & Watson [57] ABSTRACT A photometric device for generating an electric signal related to coincident light intensity comprises a number of photoresponsive means each including first and second photoconductive elements having response characteristics such that the logarithm of resistance to the logarithm of light intensity are respectively proportional over different ranges of light intensity. Additionally, the first photoconductive element in each of the photoresponsive means has a higher sensitivity than that of the second photoconductive element. The first and second photoconductive elements are posi tioned to receive light for different areas of the objective field. The first and second photoconductive element of each photoresponsive means: are specifically interconnected with similar elements of another photo responsive means to enhance the light response characteristics.

7 Claims, 7 Drawing Figures Jan. 8, 1974' PATENTEUJAH 8 1914 3783.758

sum 10$ 2 FIG. I PRIOR ART HG. 2

o PRIOR ART Dog R log L FIG. 4

FIG. 3 MR PRIOR ART PRIOR ART PATENTED JAN 8 I974 SHIT 2 0F 2 FIG. 5

FIG. 6

COMPOUND LIGHT RECEIVING ELEMENTS FOR EXPOSURE METERS BACKGROUND OF THE INVENTION The present invention relates to exposure meter cir cuitry for a photographic cameras and, more particularly, to such circuitry which uses a light receiving element comprising a number of compound photoconductiveelements having respectively different responses to low and high intensity of illumination.

.Compound light receiving elements having two pho' toconductive elements with different light intensity characteristics and resistance properties are known to the prior art. Generally one of the elements measures low intensity illumination and the other element measures high intensity illumination. Both photoconductive elements are connected in series with each other through a resistance or that photoconductive element which is responsive to low illumination is connected in series with a resistance and then connected with the other photoconductive element. Such a compound photoconductive element is illustrated in FIGS. 1 and 3 as prior art, wherein R denotes a photoconductive element which is mainly responsive to low intensity'illumination and R denotes a photoconductive element which is mainly responsive to high intensity illumination, and R denotes a resistance.

It is well known that by making use of such a compound photoconductive element as a light receiving element instead of a single photoconductive element and selecting properly the logarithmic value of resistance to the logarithmic value of the intensity of illumination on the lightreceiving plane of a respective photoconductive element and selecting a resistance, it is possible to enlarge the measuring range as shown in FIGS. 2 and 4.

However, in an exposure meter making use of such a compound photoconductive element as a light receiving element, when the partial brightness of an object in the objective field is relatively uniform and the partial I brightness ratio is close to one, a proper exposure value SUMMARY OF THE INVENTION One object of the present invention is to provide an exposure meter for a photographic camera capable of detecting lightness over a wide range of the objective field and properly controlling the exposure, and additionally controlling the exposure where the brightness distribution of an object in the objective field is not uniform.

Another object of the present invention is to provide an electronic shutter for properly controlling the exposure covering the brightness over a wide range of the objective field, and obtaining a mean brightness value and controlling the exposure where the brightness distribution of an object in the objective field is not uniform.

In order to attain the above-mentioned objects, the present invention is so constructed that a number of compound light receptive elements, each of which comprises two photoconductive elements having different illuminance resistance properties from each other, are used. One of the light receptive elements is mainly responsive to low intensity of illumination and the other element is mainly responsive to high intensity illumination. The photoconductive elements which are mainly responsive to high intensity illumination are connected in series with each other and the other photoconductive elements which are mainly responsive to low intensity illumination are connected in series to each other, respectively, through a resistance. Light rays from different field angles in the objective field of the camera are mainly incident upon each of the photoconductive elements. The brightness in the objective field of the camera is measured on the average through an electric current generated between output terminals by a respective photoconductive element and the resistance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a connection diagram showing one example of compound photoconductive elements well known in the prior art.

FIG. 2 is a graph showing the illuminance-resistance property of the compound photoconductive element of FIG 1.

FIG. 3 is a connection diagram showing another example of compound photoconductive elements well known in the prior art.

FIG. 4 is a graph showing the illuminance-resistance property of the compound photoconductive element of FIG. 3.

FIG. 5 is a connection diagram of a light receiving element in accordance with the present invention making use of two compound photoconductive elements as a light receiving element.

FIG. 6 is a side view showing the arrangement in a single lens reflex camera to obtain divisional photometry in accordance with the present invention.

FIG. 7 is another connection diagram of a light receiving element making use of two compound photoconductive elements in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Prior to the description of a preferred embodiment in accordance with the present invention, it is necessary to examine the illuminance-resistance property in the case where two photoconductive elements are used and connected in series to each other, and each respective photoconductive element divides the objective field and receives light rays from different objective fields.

Let us suppose that two photoconductive elements are connected as a single photoconductive element and the illuminance-resistance properties of the photoconductive elements are identical with each other, namely, R KL When both photoconductive elements are connected in series with each other to measure respectively different fields of an object, and provided light rays of are intensity L, and ML are incident respectively upon two single body photoconductive elements, the resistance value R (L ML connected in series between the photoconductive elements is determined as follows:

And, provided light rays of intensity M'L equal to that of both single body photoconductive elements are incident, the resistance value R (ML ML connected in series is determined as follows:

Therefore, if M M'K, however, provided M'K (1+M y)/2 (1) is satisfied, R (L ML R(ML M'L,) results.

In this manner, by connecting in series to two photoconductive elements to effect divisional photometry and averaging their outputs to satisfy formula (1 for an object having different brightness ratios, a good probable photometry of the proper exposure can be effected. As a result of our experience, the proper exposure becomes maximum in the case where 'y 0.6.

Next, the case where a compound photoconductive element is used as shown in FIG. l or FIG. 3 instead of a single photoconductive element is examined.

The compound photoconductive element comprises, for example as shown in FIG. ll, two photoconductive elements R and R having different illuminanceresistance properties. R is mainly responsive to low intensity illumination and R is mainly responsive to high intensity illumination. Fixed resistance R, is connected in series with R Photoc'onductive element R is connected in parallel thereto to generate an output electric current between both terminals thereof. And the respective logarithmic value of the resistanceilluminance property assumes an ideal slope close to a straight line shown by R and R in FIG. 2. However, as a practical matter the linearity at both ends thereof is distorted. However, for the intensity of illumination on a certain light receiving plane the resistance value of photoconductive element R is always higher than that of photoconductive element R Whereas, fixed resistance R I has a constant value regardless of the intensity of illumination on the light receiving plane, so that it is parallel with the abscissa as shown by R, in

FIG. 2.

Now, the case where a very small low intensity of illumination on the light receiving plane is examined. The resistance value of photoconductive element R is very large as compared with fixed resistance R,, and the resistance value of photoconductive element IR is larger than R so thatthe resistance value of compound photoconductive element R coincides with the resistance value of photoconductive element R As the intensity of illumination on the light receiving plane gets higher, the resistance value of photoconductive element R gets larger as compared with fixed resistance R, but the resistance value of photoconductive element R becomes comparable with the resistance value of fixed value R and when the resultant resistance value of both elements connected in series to each other is shown by a broken line, the resistance value of the compound photoconductive element takes a value close to R However, as the intensity of illuminance on the light receiving plane gets higher the value of photoconductive element R also becomes comparable with fixed resistance R and is removed from the broken line. And as the intensity of illumination on the light receiving plane gets higher it continues to increase the resistance and comes close to straight line R Thus when-the intensity of illumination becomes high it coincides with the resistance value of photoconductive element R That is, the illuminance-resistance property of compound photosensitive element R is as shown by curve R in FIG. 2.

This fact proves that the low intensity illumination range is enlarged by photoconductive element R and the high intensity illumination range is enlarged by photoconductive element R Within the enlarged intensity illumination range on the light receiving plane the ideal illuminance resistance property can be obtained. However, according to a careful observation the slope is slight in the intermediate intensity illumination range and this fact proves that 'y is changed a little in accordance with the intensity of illumination on the light receiving plane. And this fact also proves that as to the compound photoconductive element connected as shown in FIG. 3 the illuminance resistance property thereof is as shown in FIG. 4 and effects the same result as that shown in FIG. 1.

Therefore, even though two such compound photoconductive elements are merely connected in series to each other to effect divisional photometry has the same result as connecting two single photoconductive elements in series to each other as described above The formula:

which averages the brightness in the objective field by the effect of divisional photometry, is changed in accordance with the brightness in the objective field, and especially in the middle of the photometric range that change is large. Therefore, a good probable photometric result for proper exposure is impossible to be effected.

Therefore, the structure of the present invention is so arranged that as shown FIG. 5, in compound photoconductive elements R and R,, respectively include photoconductive elements R and R (which are mainly responsive to high intensity illumination) are connected in series with each other by a conductor, and photoconductive elements R and R (which are mainly responsive to low intensity illumination) are connected in series with each other through fixed resis tance R Both of the above circuits are connected in parallel with each other.

In other words, in one compound photoconductive element, photoconductive element R and photoconductive element R, are connected in series with each other and at the node thereof an external terminal is provided. In the same manner, in the other compound photoconductive element R photoconductive element R and photoconductive element R are connected in series with each other and at the node thereof an external terminal is provided, and both photoconductive elements R, and R are connected by a conductor. Photoconductive elements R and R are connected through fixed resistance R,.

And thus, both compound photoconductive elements are mounted in a camera in order that light rays from different portions of the objective field may be directed thereto as shown in FIG. 6. That is, FIG. 6 shows the essential portion-of a single lens reflex camera, wherein light rays of the objective field incident from objective lens 1 are reflected before exposure to focusing glass 3 by a movable mirror to form an image thereon. The diffused light rays thereof are incident upon pentagonal prism 5 and pass through condenser lens 4 and reflected to come into eyepiece 6. The movable mirror can be in the position at which it is at 45 to the optical axis to reflect the incident light rays to focusing glass 3 and the position at which the mirror is parallel with the optical axis to pass the incident light rays to screen On the roof plane of said pentagonal prism 5, onto the front end portion and rear end portion of the top thereof prisms 7 and 8 are adhered to let a portion of the diffused light rays from focusing glass 3 come into compound photoconductive elements R and R mounted respectively on prisms 7 and 8.

In this manner, when two photoconductive elements R and R are mounted in a camera, on account of the directive property of diffused light rays of the incident image formed upon focusing glass 3 and the distance relation between focusing glass 3 and both compound photoconductive elements R and R the light rays diffused from the left one-half portion of focusing glass 3 in FIG. 6 are mainly incident upon compound photoconductive element R, and the light rays diffused from the right one-half portion of focusing glass 3 are mainly incident upon compound photoconductive element R Thereby it is possible to attain the object of the present invention to effect photometry by dividing the light rays from the objective field.

Now, assuming that the illuminance-resistance properties of each of photoconductive elements R and R and photoconductive elements R and R of the two compound photoconductive elements R and R',, are respectively equal and satisfy the following formulas:

u Lz K1114, I, m 112 K2177 R -(L ML) Therefore, as shown in FIG. 5 and FIG. 6, the resultant resistance connected as shown in FIG. 5 in the case where light rays of the intensity of illumination L and ML are respectively incident upon two compound photoconductive elements R and R, in effecting the divisional photometrybecomes to the same resultant resistance in the case where light rays of the intensity of illumination of qual M' L are incident upon both compound photoconductive elements R and R,,.

This fact shows that in the same way as in the series connected element of two single photoconductive elements for effecting divisional photometry, two compound photoconductive elements for effecting divisional photometry by being connected as shown in FIG. 5 average objects of different brightness ratio to satisfy formulas (1) and (1) and are equal to each other. And also that in the case where light rays of an equal intensity of illumination are incident on photoconductive elements R and R',,, its resultant resistance R,,(L,, L has the following value:

(2I 1L1 l'R,z-)2I(2L 2K1L1 2K2L17+ R1 Next, the illuminance-resistance property of photoconductive elernents R and R of compound photoconductive element R shown in FIG. 1 is determined as follows:

Moreover, as in the case where light rays of the intensity of illumination L are incident upon compound And, when an equal light intensity of M 'L is incident on the two compound photoconductive elements R and R',, the following formula results:

Therefore, M M 7 However, when M (l M' )/2 (1) is satisfied, R" (L ML) RD (M'L M'L '4 1 property as that ofthe compound photoconductive elephotoconductive element R, its resultant resistance is also determined by formula (2).

Therefore, the resultant resistance of a compound photoconductive. element for divisional photometry which is connected as shown in FIG. 5 shows the same i ment shown in FIG. 1 in the case where the intensity of of different brightness ratio are incident upon compound photoconductive elements R and R',, shown in .FIG. 5 for effecting divisional photometry.

Therefore, by setting y of photoconductive elements R R R and R constituting compound photoconductive elements R, and R, to be 7 0.6, the most favorable exposure can be effected.

Further, the light receiving device composed of two compound photoconductive elements R and R shown in FIG. 7, which is the second embodiment in accordance with the present invention will be described hereinafter. Compound photoconductive elements R and R',, are mounted as shown in FIG. 6 in the same way as in the first embodiment and arranged in the finder so as to effect photometry of different upper and lower portions of an object image.

Now, assuming that light rays of the intensity of illumination L are equally incident on photoconductive elements R R,,, the resultant resistance R,,,,(L,, L of the connection shown in FIG. 7 is as follows:

This coincides with the resistance in the case where the illuminance-resistance property of photoconductive elements R and R constituting the compound photoconductive element shown in FIG. 3 is R 2K,L" R 2K [i and light rays of the intensity of illumination L, are incident upon the compound photoconductive element. That is, this fact shows that the resultant resistance of the connection such as shown in FIG. 7 has the same property as that of one compound photoconductive element shown in FIG. 3 in the case where the intensity of illumination is equal on both compound photoconductive elements R and R,

Next, the resultant resistance R (L,, ML of the connection shown in FIG. 7 in the case where the'intensity of illumination L,, ML is respectively incident upon compound photoconductive elements R and R, shown in FIG. 7 is determined as follows:

Further, from formula (3), when the intensity of illumination is equal on both compound photoconductive elements, the following formula is satisfied:

satisfying M' r (1 ments R and R,,.

This fact shows that in the same way as with two series connected single photoconductive elements for effecting divisional photometry, the connection of two compound photoconductive elements for effecting divisional photometry as shown in FIG. 7 average an object of different brightness ratio so as to satisfy formu-.

las(l)and (l) The above description is applicable for an embodiment having two compound photoconductive elements, however, compound photoconductive elements of three or more elements mounted to effect photometry for different portions of the object light rays may be used. The photoconductive elements within the three or more compound photoconductive elements, which are responsive to low intensity illumination, are connected in series with each other together with an adjusting resistance as shown in FIGS. 5 and 7 for two compound photoconductive elements. When the photoconductive elements within the three or more compound photoconductive elements, which are responsive to high intensity illumination, are connected in parallel as shown for two compound photoconductive elements in FIGS. 5 and 7, they will function the same as in the case of two compound photoconductive elements.

What I claim is:

l. A photometric converging device for generating an electric signal related to the incident light intensity, comprising:

at least two photoresponsive means each including a first photoconductive element having a responsive characteristic such that the logarithm of resistance of said first photoconductive element is proportional to the logarithm of light intensity incident thereon over a first range of light intensity, and a second photoconductive element having a responsive characteristic such that the logarithm of resistance of said second photoconductive element is proportional to the logarithm of light intensity incident thereon over a second range of light intensity, said first range of light'intensity is higher than said second light range, said first photoconductive elements being connected in series with each other, said second photoconductive elements being connected in series with each other, and each said photoresponsive means is positioned to receive light from different areas of the objective field; and

non-photoresponsive resistance means connected in series with the series connection of said second photoconductive elements and forming a branch of the circuit which is parallel to said series connection of 'said first photoconductive elements.

2. A photometric converging device as in claim l, wherein there are two of said photoresponsive means, said non-photoresponsive resistance means is c0nnected between said second photoconductive elements, and said series connection of said first photoconductive elements is connected across said series connection of said second photoconductive elements and said non-photoresponsive resistance means.

3. A photometric converging device as in claim 2, wherein the relationship between the resistance of a photoconductive element and the light intensity incident upon the light receiving surface of said photoconductive element is R KL wherein R is the resistance of the photoconductive element, L is the incident light intensity, K and y are known photometric constants, 'y is substantially the same for said first and second photoconductive elements, the K of each of said first photoconductive elements is substantially equal,

two, said non-photoresponsive resistance means is connected between said first and second photoconductive elements, and the series connection of said first photo conductive elements is connected across said nonphotoresponsive resistance means.

6. A photometric converging device as in claim 5, wherein the relationship between the resistance of a photoconductive element and the light intensity incident upon the light receiving surface of said photoconductive element is R KL' wherein R is the resistance of the photoconductive element, L is the incident light intensity, K and 'y are known photometric constants, y is substantially the same for said first and second photoconductive elements, the K of each of said first photoconductive elements is substantially equal, and the K of each of said second photoconductive elements is substantially equal.

7. A photometric converging device as in claim 6, wherein said first and second photoconductive elements in one of said photoresponsive means receive mainly light rays from one of two divided objective fields, and said first and second photoconductive elements in the other of said photoresponsive means receive mainly light rays from the other of said two divided objective fields. 

1. A photometric converging device for generating an electric signal related to the incident light intensity, comprising: at least two photoresponsive means each including a first photoconductive element having a responsive characteristic such that the logarithm of resistance of said first photoconductive element is proportional to the logarithm of light intensity incident thereon over a first range of light intensity, and a second photoconductive element having a responsive characteristic such that the logarithm of resistance of said second photoconductive element is proportional to the logarithm of light intensity incident thereon over a second range of light intensity, said first range of light intensity is higher than said second light range, said first photoconductive elements being connected in series with each other, said second photoconductive elements being connected in series with each other, and each said photoresponsive means is positioned to receive light from different areas of the objective field; and non-photoresponsive resistance means connected in series with the series connection of said second photoconductive elements and forming a branch of the circuit which is parallel to said series connection of said first photoconductive elements.
 2. A photometric converging device as in claim 1, wherein there are two of said photoresponsive means, said non-photoresponsive resistance means is connected between said second photoconductive elements, and said series connection of said first photoconductive elements is connected across said series connection of said second photoconductive elements and said non-photoresponsive resistance means.
 3. A photometric converging device as in claim 2, wherein the relationship between the resistance of a photoconductive element and the light intensity incident upon the light receiving surface of said photoconductive element is R KL wherein R is the resistance of the photoconductive element, L is the incident light intensity, K and gamma are known photometric constants, gamma is substantially the same for said first and second photoconductive elements, the K of each of said first photoconductive elements is substantially equal, and the k of each of said second photoconductive elements is substantially equal.
 4. A photometric converging device as in claim 3, wherein said first and second photoconductive elements in one of said photoresponsive means receive light rays primarily from one of two divided objective fields, and said first and second photoconductive elements in the other of said photoresponsive means receive light rays primarily from the other of said two divided objective fields.
 5. A photometric converging device as in claim 1, wherein said number of photoresponsive elements is two, said non-photoresponsive resistance means is connected beTween said first and second photoconductive elements, and the series connection of said first photoconductive elements is connected across said non-photoresponsive resistance means.
 6. A photometric converging device as in claim 5, wherein the relationship between the resistance of a photoconductive element and the light intensity incident upon the light receiving surface of said photoconductive element is R KL wherein R is the resistance of the photoconductive element, L is the incident light intensity, K and gamma are known photometric constants, gamma is substantially the same for said first and second photoconductive elements, the K of each of said first photoconductive elements is substantially equal, and the K of each of said second photoconductive elements is substantially equal.
 7. A photometric converging device as in claim 6, wherein said first and second photoconductive elements in one of said photoresponsive means receive mainly light rays from one of two divided objective fields, and said first and second photoconductive elements in the other of said photoresponsive means receive mainly light rays from the other of said two divided objective fields. 